The long term research goal is to understand the control of coronary blood flow in physiologic and pathologic circumstances. Particular emphasis is placed on the autonomic (including reflex and central nervous system) control of the coronary circulation, and the interrelation between autonomic and metabolic factors. The rationale of the proposed research is to design experiments where the major determinants of coronary blood flow are controlled or "accounted for" so that definitive answer may be obtained. Specific aims include examination of intercoronary reflexes and reflex control of the coronary circulation from somatic and visceral afferents. The central nervous system will be explored with stimulating electrodes to observe what structures are important in coronary control. Coronary artery beta receptors will be studied using a potassium arrested heart preparation to determine if beta receptors are type 1 (cardiac) or type 2 (vascular). The sympathetic innervation of coronary beta receptors will also be studied. A group of experiments will study the autonomic and reflex control of coronary blood flow and myocardial oxygen tension in hearts with partially stenosed coronary arteries, which resembles the narrowing due to atherosclerosis. Further improvements are planned for a cannula tip coronary flowmeter which has been developed in the laboratory.